feat(antdsite): add margin-bottom to title.

Author: wangyi7099

packages/antdsite/src/assets/markdown.less

@@ -41,8 +41,8 @@
   font-weight: 500;
   clear: both;
   margin-top: -3.6rem;
+  margin-bottom: 0.6rem;
   padding-top: 4.6rem;
-  margin-bottom: 0;
 }
 
 .markdown h2 {